The art of click-type torque wrenches is old and highly developed. Click-type torque wrenches are those torque-indicating wrenches which, when used, emit an audible "click" or striking sound when a predetermined force is exerted through the wrenches onto related work, such as screw fasteners.
Click-type wrenches characteristically include elongate tubular lever arms with front and rear ends. The rear ends of the lever arms are provided with or define manually engageable handles. Work-engaging heads are positioned immediately forward the front ends of the lever arms and have work-engaging parts or portions such as fastener-engaging sockets or socket-engaging projections. The heads have elongate crank arms that project freely rearwardly into and through the forward portions of the lever arms. The forward portions of the cranks are pivotally connected to the forward ends of the lever arms; are normally concentric with the lever arms and are pivoted, when actuated, so that their rear ends strike and stop against inside surfaces of the lever arms and generate or emit an audible sound.
The cranks are releasably held concentric in the lever arms by spring-loaded cam mechanisms within the lever arms rearward of the cranks.
Though the spring-loaded cam mechanisms employed by different manufacturers of click-type wrenches have varied considerably throughout the years, the most common and widely employed cam mechanisms in use today include flat-faced cam blocks normally establishing flat seated engagement with and between flat axially-disposed front and rear cam seats at the rear ends of the cranks and at the forward ends of elongate shiftable, spring-loaded slide blocks in the lever arms. The slide locks are urged forwardly by spring pressure to normally yieldingly hold the cam blocks and cam seats in seated, unactuated positions. When predetermined operating forces are exerted between the wrenches and related pieces of work, the cam blocks are caused to rock or turn between the cam seats and thus permit the cranks to pivot laterally and to strike the insides of the lever arms.
The spring-loaded slide blocks are acted upon by elongate helical compression springs with front and rear ends positioned in the rear ends of the lever arms with their front ends engaging the slide blocks. The rear ends of the springs are engaged by axially adjustable screw mechanisms which are operable to bias the springs axially to exert any desired and/or suitable force onto and through the cam means and to adjust and/or set the wrenches to actuate at any desired operating force, within the operating ranges of the wrenches.
Typically, the screw mechanisms include elongate, axially-shiftable adjusting screws with front and rear ends threadedly engaged through anchor blocks fixed in the rear end portions of the lever arms. The front ends of the adjusting screws are suitably, drivingly coupled or related to the rear ends of the springs and their rear ends are accessible at the rear ends of the lever arms to effect their being turned to effect adjustment of the springs.
Some click-type torque wrenches provided by the prior art are characterized by special and unique cam mechanisms which are distinct from the cam mechanisms briefly described above. In other wrench structures of the character here concerned with, secondary or intermediate pivoted links are provided between the cam mechanisms and the cranks. Such special and unique features and details as might be found in the art in no way alter or affect the present invention. The present invention is concerned with and is limited to that means or mechanism which is provided to effect turning of the adjusting screws at the rear ends of the lever arm of any click-type torque wrench.
Throughout the years, the prior art has sought to provide and to incorporate in click-type torque wrenches manually-operable adjusting mechanisms by which the adjusting screws of the wrenches can be turned to bias the springs in the wrenches to any desired extent and to set the operating forces of the wrenches at selected predetermined force or forces. Typically and substantially all such manually-operable adjusting mechanisms have included a manually-engageable enlargement, accessible at the exterior of the wrench lever arms, at the rear end portions thereof. The enlargements establish axially-shiftable rotary-driving engagement with the adjusting screws. Further, the enlargements typically include calibrations and indicating marks or pointers which cooperate with force-indicating calibrations on or carried by the lever arms.
As a result of the manner in which click-type wrenches are used and the abuse to which they are often times subjected, most, if not all, of the manually-operable adjusting mechanisms provided by the prior art have, to varying degrees, been found and proven to be notably undesireable and/or deficient in certain respects.
For example, in U.S. Pat. No. 3,165,041, issued Jan. 12, 1965, for "Predetermined Torque Release Wrench", a manually-operable adjusting mechanism including a handgrip-type sleeve is rotatably engaged about the rear end of the wrench lever arm. The rear end of the sleeve is drivingly coupled to the rear end of the adjusting screw. The front end of the sleeve is calibrated and cooperates with related calibrations on the lever arm. The sleeve, when not used to adjust the wrench, is held against rotation relative to the lever arm by a manually-releasable ball and detent locking mechanism. In operation and use, the above noted patented structure proved unsatisfactory since the ball and detent locking means was unable to withstand the turning forces exerted onto and through the sleeve during normal use of the wrench structure and that mechanism was so located that accidental release of the locking mechanism was a common experience.
Also, for example, in U.S. Pat. No. 3,581,606, issued June 1, 1971, for "Torque Wrench", a manually-operable adjusting mechanism, including an elongate manually-operable operating knob, was provided adjacent the rear end of the lever arm. The knob carried a calibrated sleeve that slidably entered the rear end of the lever arm and established driving engagement with the adjusting screw. The operating knob of this patented wrench structure proved to be an undesirable obstacle to the safe and effective use of the wrench structure. Specifically, the operators of that wrench structure all too frequently gripped the knob and pulled it out when putting the wrench to normal use. As the knob pulled out, proper manual purchase on the wrench structure was lost and the wrench structure was inevitably moved out of adjustment.
To the best of our knowledge and belief, the most effective and desirable manually-operable adjusting mechanism for click-type torque wrenches provided by the prior art is that adjusting mechanism disclosed in U.S. Pat. No. 3,772,942, issued Nov. 20, 1973, for "Adjustable Torque Wrench." That patented adjusting mechanism includes a strong, durable, molded plastic tubular handgrip, slidably engaged about and normally supported by the exterior of the lever arm, at the rear end thereof. The tubular handgrip has an elongate tubular core that slidably enters the rear end portion of the lever arm. The adjusting screw of the wrench has a polygonal nut at its rear end. The core has a rear opening or bore in which the nut is normally freely positioned and has a forward polygonal opening in which the nut establishes rotary-driving engagement when the handle and core are shifted axially rearward, relative to the lever arm. The inside of the lever arm is grooved (as by a suitable broaching operation) in its rear end portion and the rear portion of the core is formed with splines that enter the grooves when the handle and core are in their forward position and so that the handle or grip is normally locked against rotation relative to the lever arm and is unlocked and free to rotate relative to the lever arm when moved rearwardly (to disengage the splines from within the grooves). The front end of the tubular handgrip is calibrated and cooperates with calibrations on the lever arm, in accordance with common practice in the prior art.
The last above noted prior art wrench structure has been mass produced and has maintained notable commercial success for over fifteen years. Well in excess of one hundred thousand such wrenches have been sold and are in use throughout the world.
The single notable shortcoming found to exist in the above noted prior art wrench structure resides in the tendency of the splines in the grip to be sheared off and for the grip to become unlocked when, in regular use of the wrench structure, a user curls his wrists and pulls on the handgrip and lever arm with great and determined force. While such shearing off of the splines seldom occurs in wrench structures provided to operate throughout low ranges of applied force, it is not infrequent that the splines are sheared off in wrenches provided to operate throughout high ranges of applied force.
In an effort to overcome the above noted shortcoming in the noted prior art wrench structure, splines have been formed in the interior of the lever arms and grooves have been formed in exterior of the core parts of the noted locking mechanism. Thus, a greater mass of material has been provided in the molded plastic part to resist shearing. This effort provided some improvement, but rather than shearing the plastic part, the splines in the lever arms displaced material of the plastic part and collapsed the dore portion thereof when greater than anticipated or excessive turning forces were exerted upon and through the handgrip.
Since the splines and grooves in the above noted prior art structure are inside the lever arm, the mechanical advantage afforded to the turning forces applied to the exterior tubular handgrip is substantial. Further, since the core part in which the splines are formed is held captive within the lever arm, it is not free to yieldingly expand when subjected to high forces and the splines are, therefore, readily sheared off.
It is to be noted that the radial inward displacement of the core part or portion of the plastic part in the subject prior art structure is prevented by the nut part on the adjusting screw. That is the nut part on the adjusting screw supports the core when it is collapsed to a small extent which is insufficient to allow for disengagement of the splines from within their related grooves.